Transparent panel having a heatable coating

ABSTRACT

A transparent pane with a conductive coating is described. The transparent pane is electrically connected to an electrically heatable coating that extends at least over a part of the area of the pane and to at least two first electrodes provided for electrical connection to the two terminals of a voltage source. The heating field of the transparent pane includes at least one coating-free zone. The transparent pane also has at least one second electrode provided for electric connection to one terminal of the voltage source. The supply section of the transparent pane consists of at least two supply parts separated from each other, and a coupling section, which is electrically connected to the heatable coating. A method for manufacturing the transparent pane is also described.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is the US national stage of InternationalApplication PCT/EP2011/064708 filed on Aug. 26, 2011 which, in turn,claims priority to European Patent Applications EP 10175987.6 filed onSept. 9, 2010 and EP 11169654.8 filed on Jun. 11, 2011. The presentapplication may also be related to U.S. application Ser. No. 13/818,093,filed on even date herewith, which is the US National stage ofInternational Patent Application PCT/EP2011/064699filed on Aug. 26,2011.

The invention relates generically to a transparent pane having anelectrically heatable coating according to the preamble of claim 1.

Transparent panes having an electrical heating layer are well known perse and have already been described many times in the patent literature.Merely by way of example, reference is made in this regard to the Germanpublished patent applications DE 102008018147 A1 and DE 102008029986 A1.In motor vehicles, they are frequently used as windshields, since, bylaw, the central visual field must have no vision restrictions, with theexception of heating wires. By means of the heat generated by theheating layer, condensed moisture, ice, and snow can be removed in ashort time. Usually, such panes are produced as composite panes, inwhich two individual panes are bonded to each other by a thermoplasticadhesive layer. The heating layer can be applied on one of the innersurfaces of the individual panes, with, however, other structures alsoknown, wherein the heating layer is situated on a carrier that isdisposed between the two individual panes.

The heating layer is usually electrically connected to at least one pairof strip- or band-shaped collecting electrodes (“bus bars”), which areintended to introduce the heating current as uniformly as possible intothe coating and to distribute it widely. For an attractive aestheticappearance of the pane, the opaque bus bars are covered by opaquemasking strips.

In general, the specific heating output P_(spec) of a heatable coatingcan be described by the formula P_(spec)=U²/(R_(□)·D²), where U is thefeed voltage, R_(□) is the electrical sheet resistance of the coating,and D is the distance between the two bus bars. The sheet resistanceR_(□) of the coating is, with the materials currently used in industrialseries production, on the order of a few ohms per square unit of area(Ω/□).

In order to obtain a satisfactory heating output for the desired purposewith the onboard voltage of 12 to 24 volts standardly available in motorvehicles, the bus bars should have the least possible distance D betweenthem. In light of the fact that the resistance R of the heatable coatingincreases with the length of the current path and since the motorvehicle panes are usually wider than they are high, the bus bars aretypically disposed along the top and bottom pane edges such that theheating current can flow via the shorter path of the height of thewindow pane.

But, panes with an electrical heating layer block electromagneticradiation relatively strongly such that, in particular in motor vehicleswith a heatable windshield, radio data traffic can be significantlycompromised. Heatable windshields are, consequently, frequently providedwith coating-free zones (“communications windows or sensor windows”),which are quite permeable at least to certain ranges of theelectromagnetic spectrum, to thus enable trouble-free data traffic. Thecoating-free zones, on which electronic devices, such as sensors and thelike, are frequently situated, are commonly disposed in the vicinity ofthe top pane edge, where they can be well concealed by the upper maskingstrip.

However, coating-free zones compromise the electrical properties of theheating layer, affecting, at least locally, the current densitydistribution of the heating current flowing through the heating layer.Actually, they cause a highly inhomogeneous heating output distribution,with the heating output below and in the area surrounding thecoating-free zones clearly reduced. On the other hand, sites with aparticularly high current density (“hot spots”) appear, in which theheating output is highly increased. As a result, very high local panetemperatures can appear, which present a danger of burns and imposegreat thermal stresses on the panes. In addition, adhesion points ofparts mounted thereon can be loosened.

In contrast, the object of the present invention consists in improvinggeneric panes such that the pane is heatable with an at least virtuallyuniform heating output distribution. The generation of hot spots shouldbe reliably and safely prevented. This and other objects areaccomplished according to the proposal of the invention by a transparentpane with the characteristics of the independent claim. Advantageousembodiments of the invention are indicated by the characteristics of thesubclaims.

Generically, the transparent pane comprises an electrically heatable(conductive), transparent coating, which extends at least over asubstantial part of the area of the pane, in particular over its visualfield. The electrically heatable coating is electrically connected to atleast two first electrodes provided for electrical connection to the twoterminals of a voltage source such that by applying a feed voltage, aheating current flows over a heating field formed between the two firstelectrodes. Typically, the two first electrodes are implemented, in eachcase, in the form of a strip- or band-shaped electrode (collectingelectrode or collecting rail or bus bar) for the introduction and broaddistribution of the current in the heatable coating. For example, thefirst electrodes are, for this purpose, galvanically connected to theheating layer. The term “heating field” thus refers, here, to theheatable part of the electrically heatable coating that is situatedbetween the two first electrodes such that a heating current can beintroduced.

In the pane according to the invention, the heating field includes atleast one coating-free zone in which no heating layer is present. Thecoating-free zone is bounded by a zone edge formed at least in sectionsby the heatable coating. In particular, the coating-free zone has acircumferential zone edge, which is formed (completely) by the heatablecoating. The coating-free zone can be produced, for example, by maskingat the time of application of the heating layer onto a substrate or byremoval of the heating layer, for example, by mechanical or chemicalablation after application of the electrically heatable coating.

According to the proposal of the invention, the transparent pane issubstantially distinguished in that it has at least one second electrodeprovided for electrical connection to one terminal of the voltagesource, which electrode is disposed at least in sections, in particularwith only one electrode section, in the coating-free zone and iselectrically connected to the electrically heatable coating such that byapplying a feed voltage, a part of the heating current flows over aregion or section of the heating field, which is situated between thesecond electrode or the coating-free zone and the first electrodeprovided for connection to the other terminal of the voltage source.

The second electrode has at least one supply section disposed at leastin sections within the coating-free zone and one or a plurality ofconnection sections connected to the supply section, wherein theconnection sections extend, in each case, starting from the coating-freezone, at least beyond an edge section of the zone edge. This edgesection is formed by a section of the heating field that is situatedbetween the coating-free zone and the first electrode provided forconnection to the other terminal of the voltage source. Thus, thecoating-free zone and the first electrode provided for connection to theother terminal of the voltage source are situated on opposite sides ofsaid section of the heating field. Typically, the edge section of thezone edge, beyond which the connection sections extend, are situatedopposite or in the immediate vicinity of the first electrode providedfor connection to the other terminal of the voltage source. For example,said edge section of the zone edge has an at least approx. linear coursethat runs parallel to an at least approx. linear section of the firstelectrode provided for connection to the other terminal of the voltagesource. In a, for example, at least approx. rectangular coating-freezone, whose edges are disposed parallel or perpendicular to linear firstelectrodes, the heating current is introduced, for this purpose, intothe heatable coating via the edge section opposite the first electrode.This edge section has a shortest distance to the first electrodeprovided for connection to the other terminal of the voltage source.

In general, the second electrode is implemented such that the heatingcurrent can be introduced (widely) distributed into the heatablecoating. The second electrode has, for this purpose, one or preferably aplurality of connection sections that extend beyond the edge of theheatable coating bounding the coating-free zone and that areelectrically connected to the electrically heatable coating in order tointroduce the heating current (widely) distributed into the coating. Theconnection sections are, for this purpose, advantageously implementedwith free ends, in particular in the form of protrusions, which,preferably, protrude to the first electrode provided for electricalconnection to the other terminal of the voltage source. Advantageously,the connection sections are disposed evenly distributed over said edgesection, preferably lying next to each other with an equal distancetherebetween. The connection sections can be disposed, for example, likethe teeth of a comb or like a comb. This measure enables obtaining aparticularly uniform introduction of the heating current into theheatable coating. The connection sections can be disposed, inparticular, perpendicular to the edge section, beyond which they extend.

Advantageously, in the pane according to the invention, a difference inpotential can be established between the second electrode disposed atleast in sections in the coating-free zone and the first electrodeprovided for connection to the other terminal of the voltage source suchthat the current density distribution of the heating current in theheatable coating is at least virtually homogeneous. Similarly,homogenization of the heating output distribution in the heatablecoating can be obtained, by means of which, in particular, sites withreduced or increased heating output (hot spots) can be avoided.

By means of the second electrode disposed at least in sections in thecoating-free zone, the heat distribution in the heating layer can beselectively influenced. A particular advantage results from the factthat the second electrode is disposed at least with one electrodesection within the coating-free zone such that, there, no heatingcurrent fed in by the two first electrodes can flow from the heatinglayer into the second electrode. Thus, an undesired additional (e.g.,local) heating of the second electrode with the risk of formation of hotspots can be avoided. On the other hand, such an effect is typically tobe anticipated if the second electrode is, for example, applied to theheating layer around the coating-free zone.

A further advantage of the second electrode disposed at least insections in the coating-free zone results from the fact that theadhesion of a, for example, metallic printing paste to a, for example,glass substrate is typically better than to the heatable coating. Thisis true, in particular, for a silver printing paste applied in aprinting process, with which particularly good adhesion to glass can beobtained. This enables significant improvement of the durability, inparticular, the scratch resistance, of the second electrode.

A further advantage of the second electrode disposed at least insections in the coating-free zone results from the heating action of thesecond electrode within the coating-free zone. With such a design of thesecond electrode, any residue of ice or condensed water in the region ofthe coating-free zone can be prevented by the heat given off by thesecond electrode.

As already indicated, the second electrode is provided for connection toone terminal of the voltage source, with it being advantageous in thisregard for the second electrode to be electrically connected with thefirst electrode provided for connection to one terminal of the voltagesource such that the second electrode requires no separate electricalconnection to the voltage source. Alternatively, it would, however, alsobe possible for the second electrode to have a separate connection tothe voltage source. Particularly advantageously, the second electrodeand the first electrode provided for connection to one terminal of thevoltage source are, for this purpose, implemented in the form of a(single) common electrode such that the second electrode is formed by anelectrode section of the first electrode. This measure enables the paneaccording to the invention to be produced particularly simply from atechnical standpoint, in particular by a common or one and the sameprocess step.

According to the invention, the supply section connected to theconnection sections consists of at least two supply parts,(structurally) separated from each other but electrically connected toeach other. So, the second electrode is discontinuous on the two supplyparts of the supply section, i.e., the two supply parts have no touchingcontact with each other.

It is essential here that the two supply parts have, in each case, acoupling section, which is electrically connected to the heatablecoating, for example, by printing on the heatable coating. Furthermore,the two coupling sections are disposed such that they are galvanicallyconnected to each other through the heatable coating. The term “couplingsections” refers here and in the following to those regions of the twosupply parts of the supply section that are, on the one hand,electrically connected to the heatable coating and, on the other,galvanically coupled with each other. This does not, however, precludethat the supply parts, in each case, can also have other sections thatare, in fact, electrically connected to the heatable coating, but arenot galvanically coupled with the other supply part.

The second electrode thus has no contiguous structure, but is formed bythe two supply parts of the supply section separated from each other,and the electrically heatable coating between the two coupling sections,as well as the one or a plurality of connection sections.

The two coupling sections of the supply parts are, for the purpose of agalvanic coupling, disposed (directly) adjacent or abutting each other,with the two coupling sections disposed in juxtaposition and runningnear each other or opposite each other with a certain distance betweenthem. The distance between the two coupling sections is preferablyselected such that the heating current can flow at least virtuallywithout loss from charge carriers through the heatable coating from onecoupling section to the other coupling section. For example, thecoupling sections have, for this purpose, a distance between them thatis in the single-digit centimeter range or less.

To be sure, the electrical power dissipation of the electrodes duringthe energization with heating current is relatively low, however, awarming of the supply section of the second electrode, in particular inthe case that the supply section has a wound shape, cannot be precluded.Thus, local hot sites (hot spots) can possibly appear in the region ofthe supply section. By means of the division proposed here of the supplysection into at least two supply parts separated from each other, theoccurrence of such hot spots can advantageously be effectivelycounteracted since the heating current is distributed over acomparatively large area.

As has already been stated, the two coupling sections are disposedadjacent each other, whereby they can, in particular, have, in eachcase, an at least approx. linear course parallel to each other, in orderto obtain a particularly effective galvanic coupling through theelectrically conductive coating.

In particular, one of the two coupling sections (“first couplingsection”) can be connected to the first electrode provided forconnection to one terminal of the voltage source and the other couplingsection (“second coupling section”) can be connected to the one or aplurality of connection sections. This measure enables a technicallyparticularly simple realization of the divided second electrode.

Preferably, the electrodes of the transparent pane are produced in theprinting method, for example, the screen printing method, which enablesa technically particularly simple, economical, and reliable manufacture,in particular, of the two separated, but galvanically coupled supplyparts. Alternatively, it would also be possible to manufacture the twofirst electrodes and/or the second electrode, in each case, asindependent electrical components and to electrically connect them tothe heatable coating, for example, by soldering.

The second electrode has at least one supply section connected to theconnection sections, which supply section is composed, in one embodimentof the invention, of a coating portion disposed (exclusively) outsidethe coating-free zone and a zone portion disposed (exclusively) withinthe coating-free zone. Alternatively, the supply section can consistexclusively of the zone portion such that the supply section is disposedcompletely within the coating-free zone. The last-mentioned design hasthe particular advantage that the second electrode can be appliedvirtually completely on a glass substrate, for example, such that thesecond electrode has particularly good adhesion to the substrate. Inaddition, particularly advantageously, currents flowing via the heatablecoating between adjacent sections of the supply section can be avoided.

The supply section, in particular, the zone portion disposed within thecoating-free zone, of the second electrode advantageously follows atleast the edge section (or its contour) of the zone edge, beyond whichthe connection sections extend, by which means a particularly effectiveintroduction of the heating current into the section of the heatablecoating between the coating-free zone and the first electrode providedfor connection to the other terminal of the voltage source can beobtained.

For the above-mentioned heating action, it is particularly advantageousfor the supply section, in particular the zone portion, tocircumferentially follow the zone edge such that, in the region of thecomplete zone edge, heat can be given off to the coating-free zone. Inan embodiment particularly advantageous in this regard, the supplysection, in particular, the zone portion is distributed disposed overthe coating-free zone, for example, in that the circumferential zoneportion is provided with cross-connection sections such that such thatthe coating-free zone is particularly effectively heatable by the secondelectrode.

In the pane according to the invention, the second electrode can alsohave a plurality of supply sections, which, in each case, have a zoneportion disposed within the coating-free zone, wherein each zone portionis connected to one or a plurality of connection sections. This measureenables, particularly simply, the supply section to follow the contourof the coating-free zone only in certain edge sections, with, forexample, certain edge sections omitted, for instance, because they havea particularly high curvature or there is a very small distance to thefirst electrode provided for connection to the other terminal of thevoltage source, with the result of an undesired high current (unevenheating output distribution) between the second electrode and the firstelectrode.

Also, the transparent pane can have a plurality of coating-free zones,with which, in each case, a separate second electrode can be associated.Alternatively, the plurality of coating-free zones can be associated incommon with a single second electrode, which then has a plurality ofzone portions with, in each case, one or a plurality of connectionsections.

The electrically heatable coating can consist of one electricallyheatable individual layer or of a layer sequence containing such anindividual layer. In general, in the pane according to the invention,the electrical resistance of the heatable coating is dimensioned suchthat by applying a feed voltage, which is, for example, in the rangefrom 12 to 24 volts, a heating output suitable for practical applicationin the range of, for example, 300 to 1000 watts/m² is given off by theheating field. The electrical resistance of the heatable coating dependson the material used for the heating layer, for which purpose, forexample, silver (Ag) is used. For example, the electrical resistance ofthe heatable coating is in the range of 0.5 to 4 Ω/□. The conductivecoating includes an electrically conductive material, typically, a metalor metal oxide. Examples are metals with high electrical conductivity,such as silver (Ag), copper (Cu), gold (Au), aluminum (Al), ormolybdenum (Mo), metal alloys such as silver (Ag) alloyed with palladium(Pa), as well as transparent conductive oxides (TCOs). TCOs arepreferably indium tin oxide, fluoride-doped tin dioxide, aluminum-dopedtin dioxide, gallium-doped tin dioxide, boron-doped tin dioxide, tinzinc oxide, or antimony-doped tin oxide. For example, the conductivecoating consists of a metal layer such as a silver layer or asilver-containing metal alloy that is embedded between at least twocoatings of dielectric material of the type metal oxide. The metal oxidecontains, for example, zinc oxide, tin oxide, indium oxide, titaniumoxide, silicon oxide, aluminum oxide, or the like, as well ascombinations of one or a plurality thereof. The dielectric material canalso contain silicon nitride, silicon carbide, or aluminum nitride. Forexample, metal layer systems with a plurality of metal layers are used,wherein the individual metal layers are separated by at least one layermade of dielectric material. Very fine metal layers, which contain, inparticular, titanium or niobium, can also be provided on both sides of asilver layer. The bottom metal layer serves as a bonding andcrystallization layer. The top metal layer serves as a protective andgetter layer to prevent a change in the silver during the furtherprocess steps.

The conductive coating is, preferably, a transparent coating that ispermeable to the electromagnetic radiation, preferably electromagneticradiation of a wavelength of 300 to 1300 nm, in particular to visiblelight. The term “permeable” refers here to a total transmission that is,in particular for visible light, for example, >70% and, inparticular, >80%. For example, the light transmission of a motor vehiclewindshield is approx. 71%. Transparent conductive coatings are known,for example, from the published documents DE 202008017611 U1 and EP0847965 B1.

Advantageously, the layer sequence has high thermal stability such thatit withstands the temperatures of typically more than 600° C. necessaryfor the bending of glass panes without damage; however, even layersequences with low thermal stability can be provided. Such a layerconstruction is typically obtained by a succession of depositionprocedures. The conductive coating is, for example, deposited out of thegas phase directly onto a substrate, for which purpose methods known perse, such as chemical vapor deposition (CVD) or physical vapor deposition(PVD) can be used. Preferably, the conductive coating is deposited on asubstrate by sputtering (magnetron cathode sputtering). However, it isalso conceivable to apply the conductive coating first on a plasticfilm, in particular PET film (PET=polyethylene terephthalate), which isthen glued to a substrate.

The thickness of the conductive coating can vary broadly and be adaptedto the requirements of the individual case. It is essential that in atransparent flat electrical structure, the thickness of the conductivecoating must not be so great that it becomes impermeable to theelectromagnetic radiation, preferably electromagnetic radiation of awavelength of 300 to 1300 nm and, in particular, visible light. Forexample, the thickness of the conductive coating is at any point in therange from 30 nm to 100 μm. In the case of TCOs, the layer thickness is,for example, in the range from 100 nm to 1.5 μm, preferably in the rangefrom 150 nm to 1 μm and more preferably in the range from 200 nm to 500nm. On the other hand, the two first electrodes and the second electrodehave, in each case, compared to the heatable coating, a substantiallylower electrical resistance. For example, the electrodes have, in eachcase, an electrical resistance that is in the range from 0.15 to 4ohms/meter (Ω/m), by means of which it can be achieved that the feedvoltage applied drops substantially over the heatable coating such thatthe electrodes heat up only slightly during operation and acomparatively small share of the available heating output on theelectrodes is given off as power dissipation. However, alternatively, asubstantially higher power dissipation of the second electrode can beprovided to obtain adequate heating output for heating the coating-freezone by the second electrode.

A metal such as silver (Ag), in particular in the form of a printingpaste and use in the printing method, copper (Cu), aluminum (Al),tungsten (W), and zinc (Zn), or a metal alloy can, for example, be usedas electrode material, with this list not being exhaustive. For example,the printing paste includes silver particles and glass frits. For anelectrode, made for example from silver (Ag), which is produced in theprinting method, the layer thickness is, for example, in the range from2 to 25 microns (μm), in particular in the range from 5 to 15 μm, forexample, in the range from 7 to 15 μm.

In particular, the electrodes can be produced by printing a metallicprinting paste onto the conductive coating. Alternatively, it is alsopossible to use a thin metal foil strip as an electrode, which contains,for example, copper and/or aluminum. For example, an electrical contactbetween the metal foil strip and the conductive coating can be obtainedby an autoclave process through the action of heat and pressure. Theelectrical contact can, however, also be produced by soldering or gluingwith an electrically conductive adhesive.

In general, the electrical resistance of the second electrode can bedimensioned according to the specific requirements of the respectiveapplication. It is advantageous according to the invention for thesecond electrode to have such a resistance that upon application of thefeed voltage, a difference in potential between the second electrode andthe first electrode provided for connection to the other terminal of thevoltage source occurs, by means of which it is accomplished that thecurrent density distribution of the heating current in the heatablecoating is at least virtually homogeneous. For this purpose, it can beadvantageous for the second electrode to have a supply section situated,for example, at least in sections, outside the coating-free zone, whoselength, is dimensioned, for example, by a meanderingly curved coursesuch that the second electrode has a predefinable (selectable) orpredefined electrical resistance. Since the electrical resistance riseswith an increase in length, the resistance of the second electrode canbe modified in this manner very simply by a variation in the length ofthe supply section. It can be advantageous with regard to an at leastvirtually homogeneous current density distribution of the heatingcurrent in the heatable coating, if, in particular, through lengthvariation of the supply section, the second electrode has an electricalresistance that corresponds to the electrical resistance that theheatable coating has in a surface area that is the same size as thecoating-free zone. This measure can enable obtaining a particularlyeffective homogenization of the current density distribution in theheating layer.

As already indicated, it is advantageous in the pane according to theinvention with regard to a homogeneous current density distribution inthe heating field, for the second electrode to be implemented such thatthe heating current is introduced distributed over the edge of theheatable coating bounding the coating-free zone. The second electrodecan, for example, be implemented such that the heating current isintroduced distributed at least over such an edge section of theheatable coating, that has a shortest distance, in particular a shortestperpendicular distance to the first electrode provided for connection tothe other terminal of the voltage source. With an at least approx.rectangular coating-free zone, for example, the heating current can beintroduced, for this purpose, for example, over one of the two longeredge sections or one of the two shorter edge sections, depending onwhich edge section is opposite the first electrode provided forconnection to the other terminal of the voltage source.

The pane according to the invention can, for example, be implemented asso-called single-plane safety glass (SPSG) with only one substrate or asa composite pane with, as a rule, two substrates bonded to each other bya thermoplastic adhesive layer. The substrate is made, for example, of aglass material, such as float glass, quartz glass, borosilicate glass,soda lime glass, cast glass, or ceramic glass, or of a non-glassmaterial, for example, plastic, such as polystyrene (PS), polyamide(PA), polyester (PE), polyvinyl chloride (PVC), polycarbonate (PC),polymethyl methacrylate (PMA), or polyethylene terephthalate (PET),and/or mixtures thereof. Examples of suitable glasses can be found, forexample, in European Patent EP0847965 B1. In general, any material withsufficient chemical resistance, suitable shape and size stability, aswell as, optionally, adequate optical transparency can be used.Depending on the application, the thickness of the substrate can varywidely. For a heatable, transparent glazing, the thickness of thesubstrate is, for example, in the range from 1 to 25 mm, whereas,typically, for transparent panes, a thickness of 1.4 to 2.1 mm is used.The substrate is planar or curved in one or a plurality of spatialdirections. In the case of a composite pane, the heatable coating isdisposed on at least one surface, for example, on the surface of theinner pane facing the outer pane and/or on a surface of a carrierdisposed between the two individual panes. For example, the paneaccording to the invention is implemented in the form of a motor vehiclewindshield, with the coating-free zone disposed, for example, adjacentor in the vicinity of a top pane edge of the windshield in the installedstate, by means of which a simple concealment of the coating-free zoneis possible using an opaque cover element implemented, for example, as ablack screen-printed edge.

The invention further extends to a method for producing a transparentpane, in particular, as stated above. The method comprises the followingsteps:

-   -   producing an electrically heatable coating, which extends at        least over a substantial part of the area of the pane, in        particular, over its visual field;    -   forming at least two first electrodes provided for electrical        connection to the two terminals of a voltage source, which        electrodes are electrically connected to the heatable coating        such that by applying a feed voltage, a heating current flows        over a heating field situated between the two first electrodes;    -   producing at least one coating-free zone in the heating field,        which is bounded by a zone edge formed at least in sections by        the heatable coating;    -   producing at least one second electrode provided for electrical        connection to one terminal of the voltage source, which        electrode runs at least in sections in the coating-free zone and        is electrically connected to the heatable coating such that a        part of the heating current flows over a section of the heating        field that is situated between the second electrode and the        first electrode provided for connection to the other terminal of        the voltage source. The second electrode is produced such that        it has at least one supply section disposed at least in sections        within the coating-free zone and one or a plurality of        connection sections, wherein the connection sections extend, in        each case, starting from the coating-free zone, beyond an edge        section of the zone edge, wherein the edge section is formed by        a section of the heating field, which is situated between the        coating-free zone and the first electrode provided for        connection to the other terminal of the voltage source.        Typically, the second electrode is implemented such that it has        at least one supply section disposed at least in sections        outside the coating-free zone and a plurality of connection        sections, wherein the connection sections are distributed        disposed at least over an edge section of the edge bounding the        coating-free zone, which edge is opposite the first electrode        provided for connection with the other pole of the voltage        source, and electrically connected to the heatable coating. The        supply section is formed from at least two supply parts        separated from each other, which have, in each case, a coupling        section electrically connected to the heatable coating, with the        two coupling sections disposed opposite each other such that        they are galvanically coupled by the heatable coating.

In an advantageous embodiment of the method according to the invention,the second electrode and the first electrode provided for electricalconnection to one terminal of the voltage source are produced, forexample, by printing, in particular screen printing, together in one andthe same process or printing step.

The invention further extends to the use of a pane as described above asa functional and/or decorative individual piece and as a built-in partin furniture, devices, and buildings, as well as in means oftransportation for travel on land, in the air, or on water, inparticular in motor vehicles, for example, as a windshield, rear window,side window, and/or glass roof. Preferably, the pane according to theinvention is implemented as a motor vehicle windshield or a motorvehicle side window.

It is understood that the aforementioned characteristics and those to beexplained in the following can be used not only in the combinationsindicated, but also in other combinations or alone, without departingfrom the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now explained in detail using exemplary embodimentswith reference to the accompanying figures. They depict, in simplified,not to scale representation:

FIG. 1 a top view of an exemplary embodiment of the motor vehiclewindshield according to the invention;

FIG. 2 a perspective cross-sectional view of a detail of the windshieldof FIG. 1;

FIGS. 3-8 different variants of the windshield of FIG. 1;

FIG. 9A-9B another variant of the windshield of FIG. 1 with adiscontinuous supply section;

FIG. 10-11 variants of the windshield of FIGS. 9A and 9B;

FIG. 12 a variant of the windshield of FIG. 7.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is first made to FIGS. 1 and 2, in which a transparentwindshield of a motor vehicle, referred to as a whole by the referencecharacter 1, is depicted. FIG. 1 presents a view of the windshield 1from the inside. The windshield 1 is implemented here, for example, as acomposite pane, whose construction is discernible in the perspectivesectional view of FIG. 2.

According to it, the windshield 1 comprises two rigid individual panes,namely, an outer pane 2 and an inner pane 3, which are fixedly bonded toeach other by a thermoplastic adhesive layer 4, in this case, forexample, a polyvinyl butyral film (PVB), ethylene vinyl acetate film(EVA), or polyurethane film (PU). The two individual panes 2, 3 areapproximately the same size and shape and can, for example, have atrapezoidal curved contour, which is not depicted in detail in thefigures. They are, for example made of glass, but can also be producedfrom a non-glass material, such as plastic. For applications other thanas a windshield, it would also be possible to produce the two individualpanes 2, 3 from a flexible material. The contour of the windshield 1 isdefined by a pane edge 5 common to the two individual panes 2, 3, withthe windshield 1 having, at the top and bottom, two opposing first sides6, 6′ as well as, on the left and on the right, two opposing secondsides 7, 7′.

As depicted in FIG. 2, a transparent, electrically heatable coating 8 isdeposited on the side of the inner pane 3 bonded to the adhesive layer4. Here, the heatable coating 8 is, for example, applied substantiallyon the entire surface of the inner pane 3, with an edge strip 9 of theinner pane 3 circumferential on all sides not coated such that a coatingedge 10 of the heatable coating 8 is set back inward relative to thepane edge 5. This effects electrical isolation of the heatable coating 8toward the outside. In addition, the heatable coating 8 is protectedagainst corrosion penetrating from the pane edge 5.

The heatable coating 8 comprises, in a manner known per se, a layersequence (not shown in detail) with at least one electrically heatable,metallic sublayer, preferably silver (Ag), and, optionally, othersublayers such as anti-reflection layers and blocker layers. The layersequence advantageously has high thermal stability such that itwithstands , without damage, the temperatures of typically more than600° C. necessary for the bending of glass panes; however, layersequences with low thermal stability can also be provided. The heatablecoating 8 can also be applied as a metallic single layer. It is alsoconceivable not to apply the heatable coating 8 directly on the innerpane 3, but instead to apply it first on a carrier, for example, aplastic film that is subsequently bonded with the outer and inner pane2, 3. Alternatively, the carrier film can be bonded to adhesive films(e.g., PVB films) and bonded as a three layer arrangement (trilayer) toinner and outer pane 2, 3. The heatable coating 8 is preferably appliedby sputtering over magnetron cathode sputtering onto the inner or outerpane 2, 3.

As depicted in FIG. 1, the heatable coating 8 is electrically connectedadjacent the two first sides 6, 6′, i.e., at the top and bottom paneedge 5, to a band-shaped top collecting electrode 11 (bus bar) and aband-shaped bottom bus bar 11′ (referred to in the introduction of thedescription as “first electrodes”) and, for example, for this purpose,galvanically coupled to the two bus bars 11, 11′. The top bus bar 11 isprovided for connection to one terminal of a voltage source (not shown),whereas the bottom bus bar 11′ is provided for connection to the otherterminal of the voltage source. The two bus bars 11, 11′ of oppositepolarity serve for uniform introduction and distribution of the heatingcurrent in the heatable coating 8, with a heatable section or heatingfield 12 enclosed between the two bus bars 11, 11′. The two firstelectrodes 11, 11′ are, for example, printed onto the electricallyheatable coating 8. The two bus bars 11, 11′ have, in each case, an atleast approx. linear course.

The windshield 1 is further provided with a coating-free zone 14, whichserves here, for example, as a sensor window for a rain sensor. It isunderstood that the coating-free zone 14 can also be provided for adifferent use, for example, as a communication window, for whichpurpose, it is permeable at least to a part of the electromagneticspectrum in order to enable trouble-free data traffic through thewindshield.

The coating-free zone 14 has, for example, here, an at least approx.rectangular contour with rounded corners and is bounded by a zone edge18 formed by the electrically heatable coating 8. The coating-free zone14 is permeable at least to part of the electromagnetic spectrum (e.g.,IR-waves, radio waves in the ultrashort, short, and longwave range) inorder to enable trouble-free data traffic through the windshield 1. Thecoating-free zone 14 can, for example, be produced by masking prior toapplication of the heatable coating 8 on the inner pane 3.Alternatively, it can also be produced after application of the heatablecoating 8 by chemical or mechanical ablation, for example, by means ofetching or use of a friction wheel. The coating-free zone 14 is situatedwithin the heating field 12 in the vicinity of the top bus bar 11.

As depicted in FIG. 1, an additional electrode 15 (referred to in theintroduction of the description as “second electrode”) is provided inthe windshield 1, which is, for example, electrically (galvanically)connected here to the top bus bar 11. The additional electrode 15 can,at least theoretically, be divided into various sections. Thus, theadditional electrode 15 includes a supply section 16 electricallyconnected to the top bus bar 11, which here has, for example, at thebeginning in one coating portion 25 a meanderingly curved course and,then, transitions into a circumferential, at least approx. ring-shapedzone portion 17. Whereas the coating portion 25 is situated completelyin the region of the heatable coating 8, the zone portion 17 is disposedcompletely within the coating-free zone 14. The zone portion 17 isimplemented, for example, at least approx. congruent to the contour ofthe zone edge 18. Thus, within the zone portion 17 of the supply section16, a free area or electrode window 26 bounded by the zone portion 17 isformed such that the function of the coating-free zone 14 is notcompromised by the additional electrode 15.

The zone edge 18 bounding the coating-free zone 14 is composed of twoopposing, at least approx. straight edge sections 19, 19′, which lieparallel to the first sides 6, 6′ of the windshield 1, and two opposing,at least approx.

straight second edge sections 20, 20′, which lie parallel to the secondsides 7, 7′ of the windshield 1. In particular, a top first edge section19 is disposed closer to the top bus bar 11 than to the bottom bus bar11′, whereas a bottom first edge section 19′ is disposed closer to thebottom bus bar 11′ than to the top bus bar 11. In particular, the bottomfirst edge section 19′ runs parallel to the bottom bus bar 11′, which isprovided for connection to the other terminal of the voltage source.

The additional electrode 15 further has a plurality of linear runningconnection sections 21, which are implemented, in each case, as aprotrusion of the ring-shaped zone portions 17 of the supply section 16.Here, the connection sections 21 are distributed disposed (only) in theregion of the bottom first edge sections 19′. The connection sections 21are disposed in uniform succession (equal distance between them)row-like or comb-like next to each other, protrude, in each case,perpendicular to the bottom first edge section 19′ toward the bottom busbar 11′, and extend, in each case, all the way to the heatable coating 8such that they are electrically (galvanically) connected thereto. Theconnection sections 21 thus extend beyond the bottom first edge section19′. On the two ends of the row, the connection sections 21 are slightlyinclined toward the second sides 7 of the windshield 1, being pointedroughly toward the left bottom corner region 22 or the right bottomcorner region 22′ of the windshield 1. The connection sections 21 aredisposed evenly distributed over the complete length of the bottom firstedge section 19′ and thus enable uniform introduction and (wide)distribution of the heating current in the bottom region of the heatingcoating-free zone 14 into the heatable coating 8.

The two band-shaped bus bars 11, 11′ are produced here, for example, byprinting, for example, using screen printing methods, a metallicprinting paste, for example, silver printing paste, onto the heatablecoating 8. The additional electrode 15 can equally be produced as aband-shaped electrode by printing onto the heatable coating 8 and thecoating-free zone 14, with the two bus bars 11, 11′ and the additionalelectrode 15 produced here, for example, in a common (same) process orprinting step. Alternatively, it would also be possible to produce thebus bars 11, 11′ and/or the additional electrode 15 through theapplication of prefabricated metal strips made, for example, of copperor aluminum, which are then electrically connected, for example, bysoldering to the heatable coating 8.

The two bus bars 11, 11′ and the additional electrode 15 have here, forexample, an electrical resistance in the range from 0.15 to 4 ohm/meter(Ω/m). The specific resistance is, in particular, for bus bars 11, 11′produced in the printing method, for example, in the range from 2 to 4μohm·cm. The width of the two band-shaped bus bars 11, 11′ is, forexample, 10 to 15 mm. The width of the band-shaped additional electrode15 is, for example, less than 10 mm and is, for example, 1 to 10 mm. Thewidth of the two bus 11, 11′ and the additional electrode 15 isdimensioned, for example, such that they, in each case, give off amaximum of 10 W/m, preferably a maximum of 8 W/m, for example, 5 W/m, aspower dissipation. The thickness of the two bus bars 11, 11′ and theadditional electrode 15 is, for example, in each case, in the range from5 to 25 μm, in particular in the range from 10 to 15 μm. Across-sectional area of the two bus bars 11, 11′ and the additionalelectrode 15 is, for example, in each case, in the range from 0.01 to 1mm², in particular in the range from 0.1 to 0.5 mm².

For prefabricated band-shaped bus bars 11, 11′ made, for example, ofcopper (Cu), and correspondingly implemented additional electrode 15,the thickness is, for example, in the range from 30 to 150 μm, inparticular in the range from 50 to 100 μm. In this case, thecross-sectional area is, for example, in the range from 0.05 to 0.25mm².

Preferably, the additional electrode 15 in the windshield 1 has anelectrical resistance such that upon applying the feed voltage, theheating current flowing through the heating field 12 has an at leastvirtually homogeneous current density distribution. The electricalresistance of the additional electrode 15 can be adjusted, in a simplemanner, through the length of the supply section 16, in particular ofthe coating portions 25, to a freely selectable pre-definable orpredefined resistance value, for which purpose, the supply section 16here has, for example, a meandering course; however, a different coursecan equally be realized.

The electrical sheet resistance of the heatable coating 8 is, forexample, selected such that the current flowing through the heatingfield 12 has a maximum magnitude of 5 A. For example, the electricalsheet resistance of the heatable coating 8 is in the range from 0.1 to 4Ω/□ and is, for example, 1 Ω/□.

The surface of the outer pane 2 facing the inner pane 3 is provided withan opaque color layer that forms a frame-shaped circumferential maskingstrip 13 on the pane edge 5. In FIG. 1, the masking strip 13 is depictedonly in the region of the two first sides 6, 6′ of the windshield 1. Themasking strip 13 is made, for example, from an electrically insulating,black-colored material that is baked into the outer pane 2. On the onehand, the masking strip 13 prevents seeing an adhesive strand (notshown), with which the windshield 1 is glued into the motor vehiclebody; on the other, it serves as UV protection for the adhesive materialused. Moreover, the masking strip 13 defines the visual field of thewindshield 1. A further function of the masking strip 13 is to concealthe two bus bars 11, 11′ such that they are not discernible from theoutside. On the top pane edge 5, the masking strip 13 further has acover section 23, by which the coating-free zone 14 is concealed.

In the windshield 1 with a heatable coating 8, a heating current canthus be generated in the heating field 12 by applying a feed voltage tothe two bus bars 11, 11′. By applying the feed voltage, a difference inpotential between the additional electrode 15 and the bottom bus bar 11′is simultaneously generated such that a part of the heating currentflows through a heating field section 24, which is enclosed between theadditional electrode 15 or the coating-free zone 14 and the bottom busbar 11′. In the region of the coating-free zone 14, the heating currentis introduced evenly distributed into the heatable coating 8 over thebottom first edge section 19′, which is immediately adjacent the bus bar11′ to be connected to the other terminal of the voltage source. The(internal) electrical resistance of the additional electrode 15generates, with the applied feed voltage, such a difference in potentialbetween the additional electrode 15 and the bottom bus bar 11′ that thecurrent density distribution of the heating current is at leastvirtually homogeneous in the complete heatable coating 8. Thisadvantageously enables homogenization of the heating output distributionin the heatable coating 8.

FIGS. 3 to 8 illustrate different variants of the windshield 1 ofFIG. 1. In order to avoid unnecessary repetition, only the differencesrelative to the windshield 1 of FIG. 1 are explained and reference isotherwise made to the statements made regarding FIGS. 1 and 2. In FIGS.3 to 8, for the purpose of a simpler representation, the windshield 1 isshown, in each case, only as a detail in a top region.

FIG. 3 illustrates a variant in which the supply section 16 of theadditional electrode 15 is meanderingly curved and consists of the zoneportion 17 disposed completely within the coating-free zone 14. Thecoating-free zone 14 comprises a round first zone section 28 and arectangular second zone section 29 connected thereto, which extends tothe bus bar 11 provided for connection to one terminal of the voltagesource. The meandering tracks of the zone portion 17 extend, in eachcase, between the bus bar 11 and the circular first zone section 28 andchange their course direction in a direction perpendicular thereto.Except for the connection sections 21, which extend beyond the zone edge18 and are electrically connected to the heatable coating 8, theadditional electrode 15 is thus situated completely within thecoating-free zone 14. On the one hand, this enables obtaining aparticularly good adhesion of the additional electrode 15, for example,on the glass inner pane 3. On the other, electrical currents betweenadjacent parts of the supply section 16 conducted via the heatablecoating 8 can be prevented. Such currents can occur, in particular, thecase of relatively large voltage differences between adjacent parts ofthe supply section 16, if the additional electrode 15 is applied on theheatable coating 8. Moreover, with this variant, it is possible toprevent currents introduced from the two bus bars 11, 11′ into theheatable coating 8 flowing from the heatable coating 8 to the supplysection 16 and resulting there in undesired additional (possibly local)heating with the risk of hot spots. Here, the zone portion 17 is notimplemented as a complete ring but forms only a partial ring, whichfollows the contour of the zone edge 18 of the coating-free zone 14, inparticular, in a round edge section 27, which is formed by a heatingfield section 24 that is situated between the additional electrode 15 orcoating-free zone 14′ and the bus bar 11′ provided for connection to theother terminal of the voltage source. The windshield 1 has furthercoating-free zones 14′, 14″, oval shaped here, for example, with which,in the present example, no additional electrode 15 is associated, butwhich could likewise be provided with an additional electrode 15.

FIG. 4 illustrates another variant, which differs from the variant ofFIG. 3 in that the additional electrode 15 has two supply 16, 16′ thathave a common zone portion 17. The common zone portion 17 follows thecontour of the zone edge 18, in particular, in the round edge section27, which is formed by a heating field section 24 that is situatedbetween the additional electrode 15 or coating-free zone 14′ and the busbar 11′ provided for connection to the other terminal of the voltagesource. The coating-free zone 14 consists only of the circular firstzone section 28, such that the two supply sections 16, 16′ run insections on the heatable coating 8.

The variant illustrated in FIG. 5 differs from the variant shown in FIG.4 only in that the common zone portion 17 is discontinuous such that twoadditional electrodes 15, 15′ separated from each other are formed,which have, in each case, a separate supply section 16, 16′ andconnection sections 21, 21′ connected thereto. This measure enablesintroducing a heating current through the additional electrodes 15, 15′into the heating coating 8 only in selective sections of the zone edge18. This can, for example, be advantageous when the heating currentintroduced is undesirably high due to a very short distance to the busbar 11′. It can likewise be advantageous to introduce no heating currentthrough the additional electrode 15 in a region (not shown) ofcomparatively high curvature of the zone edge 18.

The variant illustrated in FIG. 6 differs from the variant shown in FIG.4 in that the coating-free zone 14 comprises the circular first zonesection 28 and the rectangular second zone section 29 connected thereto,which extends to the bus bar 11 provided for connection to one terminalof the voltage source. The advantages of such a design have already beenexplained in the variant of FIG. 3.

The variant illustrated in FIG. 7 differs from the variant shown in FIG.3 in that the coating-free zone 14 consists only of the circular firstzone section 28. In addition, the meandering tracks of the zone portion17 extend, at times, at right angles to a connection between the bus bar11 and to the circular first zone section 28 and change their coursedirection along a path between the bus bar 11 and the circular firstzone section 28. This enables realization of relatively large distancesbetween adjacent regions of the supply section 16, whereby, inparticular, when relatively high voltages are present between adjacentregions of the supply section 16, currents conducted by the heatablecoating 8 between these regions can be prevented.

The variant illustrated in FIG. 8 differs from the variant shown in FIG.6 in that the coating-free zone 14 comprises the circular first zonesection 28 and the rectangular second zone section 29 connected thereto,which extends to the bus bar 11 provided for connection to one terminalof the voltage source. The advantages of such a design have already beenexplained in the variant of FIG. 3.

FIG. 9A depicts another variant of the windshield of FIG. 1, wherein, asa variant, the zone portion 17 17 is not circumferentially closed, but,instead, is implemented only in the region of one (right, in this case)second edge section 20′ and bottom first edge section 19′. It has beendemonstrated in practice that in the meanderingly curved coating portion25 of the supply section 15 situated on the heatable coating 8, undercertain conditions, the possibility exists that, in particular, in theregion identified by “A”, a higher temperature is present than in theheating field 12. This can be undesirable, in particular, with regard tocustomer requirements.

A measure for prevention of such local overheating is illustrated inFIG. 9B. According to it, the supply section 16 of the additionalelectrode 15′ is discontinuous and divided into two regions spatially(structurally) separate from each other, i.e., not connected to eachother by the same electrode material. Thus, the supply section 16comprises a first supply part 30 and a second supply part 31 separatetherefrom. The first supply part 30 is connected to the (top) first busbar 11 provided for connection to one terminal of the voltage source.The second supply part 31 comprises the zone portion 17, from which theconnection sections 21 protrude. In addition, the first supply part 30includes a first coupling section 32; the second supply part 30 includesa second coupling section 33, which are, in each case, electricallyconnected to the electrically conductive heatable coating 8, forexample, by printing on to the coating 8. Each of the two couplingsections 32, 33 has an at least approx. linear course, with the twocoupling sections 32, 33 running close to each other in parallelalignment directly adjacent each other in a coupling zone 34. A distanceB between the two coupling sections 32, 33 in the coupling zone 34 isselected such that the two coupling sections 32, 33 are galvanicallyconnected (coupled) by the electrically heatable coating 8. When the(top) bus bar 11 provided for connection to one terminal of the voltagesource is impinged on by a heating voltage, the heating current can betransferred between the two coupling sections 32, 33 by the heatablecoating 8 situated between the two coupling sections 32, 33. The coating8 thus forms a current transfer zone 35 between the two couplingsections 32, 33 for current transfer between the two coupling sections32, 33. A distance B between the two coupling sections 32, 33 ispreferably selected such that the current can be transferred virtuallywithout loss on charge carriers between the two coupling sections 32,33. Here, the distance B is, for example, in the single-digit centimeterrange or less.

FIG. 10 illustrates, using a schematic depiction, the divided additionalelectrode 15′ of FIG. 9B in the installed state, with the windshield 1identical in structure to the windshield 1 illustrated in FIGS. 1 and 2,with the exception of the divided additional electrode 15′. In order toavoid unnecessary repetition, reference is made in this regard to thestatements made there. In contrast to FIG. 9B, the additional electrode15′ includes a ring-shaped close zone portion 17 in the supply section16. The connection sections 21 are not depicted for the purpose of asimpler representation. The two linear coupling sections 32, 33 aredisposed such that they have a course perpendicular to the two linearbus bars 11, 11′, at least approx. parallel to each other.

FIG. 11 depicts a variant of FIG. 10, in which only the two couplingsections 32, 33 are disposed opposite each other and extend parallel toeach other as well as parallel to the two linear bus bars 11, 11′.

The variant illustrated in FIG. 12 differs from the variant shown inFIG. 7 in that the supply section 16 of the additional electrode 15′ isdiscontinuous and divided into two regions spatially (structurally)separated from each other, i.e. not connected to each other by the sameelectrode material. The supply section 16 comprises a first supply part30 and a second supply part 31 separate therefrom. The first supply part30 is connected to the (top) first bus bar 11 provided for connection toone terminal of the voltage source. The second supply part 31 comprisesthe zone portion 17, from which the connection sections 21 protrude. Thefirst supply part 30 includes a first coupling section 32; the secondsupply part 30 includes a second coupling section 33, which are, in eachcase, electrically connected to the electrically conductive heatablecoating 8. Each of the two coupling sections 32, 33 has an at leastapprox. linear course, with the two coupling sections 32, 33 runningclose to each other in parallel alignment directly adjacent each otherin a coupling zone 34. The two coupling sections 32, 33 are galvanicallyconnected (coupled) in the coupling zone 34 by the electrically heatablecoating 8. The coating 8 thus forms a current transfer zone 35 betweenthe two coupling sections 32, 33 for the current transfer between thetwo coupling sections 32, 33. The two coupling sections 32, 33 aredisposed opposite each other and extend parallel to the two linear busbars 11, 11′.

LIST OF REFERENCE CHARACTERS

-   1 windshield-   2 outer pane-   3 inner pane-   4 adhesive layer-   5 pane edge-   6, 6′ first side-   7, 7′ second side-   8 coating-   9 edge strip-   10 coating edge-   11, 11′ bus bar-   12 heating field-   13 masking strip-   14, 14′, 14″ coating-free zone-   15, 15′ additional electrode-   16, 16′ supply section-   17, 17′ zone portion-   18 zone edge-   19, 19′ first straight edge section-   20, 20′ second straight edge section-   21, 21′ connection section-   22, 22′ corner region-   23 cover section-   24 heating field section-   25 coating portion-   26 electrode window-   27 round edge section-   28 first zone section-   29 second zone section-   30 first supply part-   31 second supply part-   32 first coupling section-   33 second coupling section-   34 coupling zone-   35 current transfer zone

The invention claimed is:
 1. A transparent pane comprising anelectrically heatable coating electrically connected to at least twofirst electrodes provided for electrical connection to two terminals ofa voltage source such that by applying a feed voltage, a heating currentflows over a heating field formed between the at least two firstelectrodes, wherein the heating field includes at least one coating-freezone, which is bounded by a zone edge formed at least in sections by theelectrically heatable coating, characterized by at least one secondelectrode provided for electrical connection to one terminal of thevoltage source, the at least one second electrode having at least onesupply section disposed at least in sections in the at least onecoating-free zone and at least one connection section connected to theat least one supply section, wherein the at least one connection sectionextends starting from the at least one coating-free zone, beyond an edgesection of the zone edge, the edge section being formed by a section ofthe heating field that is situated between the at least one coating-freezone and one of the at least two first electrodes provided forconnection to a second one of the two terminals of the voltage source,and wherein the at least one supply section is discontinuous andconsists of at least two supply parts spatially separated from eachother and not connected to each other by the same electrode material asthe two supply parts,which have a respective coupling sectionelectrically connected to the electrically heatable coating, the twocoupling sections being disposed such that they are galvanically coupledby the electrically heatable coating.
 2. The transparent pane accordingto claim 1, wherein the two coupling sections have an approximatelyparallel course.
 3. The transparent pane according to claim 1, wherein afirst coupling section is connected to one of the at least two firstelectrodes provided for connection to one of the two terminals of thevoltage source and a second coupling section is connected to the atleast one connection sections.
 4. The transparent pane according toclaim 1, wherein the at least one connection section is provided with afree end.
 5. The transparent pane according to claim 1, wherein the atleast one connection section is implemented evenly distributed over theedge section of the at least one coating-free zone.
 6. The transparentpane according to claim 1, wherein the at least one supply section iscomposed of a coating portion disposed outside the at least onecoating-free zone and a zone portion disposed within the at least onecoating-free zone.
 7. The transparent pane according to claim 1, whereinthe at least one supply section is disposed completely within the atleast one coating-free zone.
 8. The transparent pane according to claim1, wherein the at least one supply section follows at least the edgesection of the zone edge, beyond which the at least one connectionsection extends.
 9. The transparent pane according to claim 1, whereinthe at least one supply section circumferentially follows the zone edge.10. The transparent pane according to claim 1, wherein the at least onesupply section is disposed over the at least one coating-free zone. 11.The transparent pane according to claim 1, wherein the at least onesecond electrode has at least two supply sections, which are connectedto the at least one connection section.
 12. The transparent paneaccording to claim 1, wherein a length of the at least one supplysection is dimensioned in order to provide the at least one secondelectrode with a predefined electrical resistance.
 13. A method forproducing a transparent pane, comprising: providing an electricallyheatable coating, forming at least two first electrodes for electricalconnection to two terminals of a voltage source, the at least two firstelectrodes being electrically connected to the electrically heatablecoating such that by applying a feed voltage, a heating current flowsover a heating field situated between the two first electrodes,providing at least one coating-free zone in the heating field,andproviding at least one second electrode for electrical connection to oneterminal of the voltage source, the at least one second electrode havingat least one supply section disposed at least in sections in the atleast one coating-free zone and the at least one connection sectionconnected to the at least one supply section, wherein the at least oneconnection section extends starting from the at least one coating-freezone, beyond an edge section of the zone edge, wherein the edge sectionis formed by a section of the heating field, which is situated betweenthe at least one coating-free zone and one of the at least two firstelectrodes provided for connection to the other one of the two terminalsof the voltage source, wherein the at least one supply section isdiscontinuous and is formed from at least two supply parts spatiallyseparated from each other and not being connected to each other by thesame electrode material as the two supply parts, which have a respectivecoupling section electrically connected to the electrically heatablecoating, and wherein the coupling sections are disposed such that theyare galvanically coupled by the electrically heatable coating.
 14. Themethod according to claim 13, wherein the at least one first electrodeand the at least one second electrode are produced in a printing method.15. The transparent pane according to claim 5, wherein two or moreconnection sections are implemented like a comb.
 16. The transparentpane according to claim 12, wherein the predefined electrical resistanceis equivalent to the sheet resistance of the heatable coating in asurface area that corresponds to the at least one coating-free zone. 17.The method according to claim 14, wherein the printing method is screenprinting.